Electrolytic method for producing oxygen



Dec. 11, 1945. M. JANES ELECTROLYTIC METHOD FOR PRODUCING OXYGEN FiledNOVFB, 1941 ZZVAVl/AY/l A 4\\ v H .W Wm ma 9 W M wxkwimifir1W:mW m m m lm ATTORNEY stantial production 01 hydrogen peroxide.

Patented Dec. 11, 1945 OFFICE Milton Janes, Lakewood, Ohio, as'signor toNav I I tional' Carbon Compan New York y, Inc., a corporation ofApplication November 8, 1941, Serial No. 418,390

3 Claims.

. Electrolysis of aqueous solutions of caustic alkalisor ofoxygen-containing acids has been used as a method of obtaining very purehydrogen and oxygen. The best known types of commercial cells for thispurpose comprise electrodes of irongroup metal, usually of nickel-platediron, separated by an asbestos cloth diaphragm, and as an electrolyte asolution of sodium hydroxide or potassium hydroxide in a concentrationbetween 10% and 35%. Published data indicate that such cells can produceabout 150 grams of oxygen per kilowatt-hour. Considered solely as asource of oxygen, electrolysis is so much more costly thanair-separation methods that it has not competed with the latter methods;rather, it has been used as a source of pure hydrogen, the oxygen beinga by-product.

The electrolytic production of oxygen offers some attractive advantages.The necessary equipment is relatively simple, inexpensive, small involume, and durable, and requires little labor in operation andmaintenance. The cost of the electrical energy is, in fact, the mainimpediment which has prevented the more widespread use of theelectrolytic method. Another item of expense, which under somecircumstances is material, is the cost of distilled water which isconsumed in the process.

It is the principal object of the present invention to increase theyield of oxygen per unit of electrical energy consumed in theelectrolytic production of oxygen. Another object is to provide anelectrolytic method for producing oxygen, in which no hydrogen gas isliberated and which consumes no water. A further object is to producepure oxygen by the electrolysis of aqueous caustic solutions without theuse of an interelectrode diaphragm. Another object is a method, capableof producing per unit of electrical energy from two to two and one half,or even -more, times as much oxygen as is produced by electrolyticmethods and apparatus heretofore used commercially. Still another objectis an electrolytic method which consumes little or no water byelectrolysis.

The principal feature of the invention is the use of a continuouslydepolarized cathode, suitably an air-depolarized porous carbon cathode,in

combination with an insoluble or passive anode in an aqueous electrolyteof potassium hydroxide or sodium hydroxide. I have found that, atconvenient current densities, not only is no hydrogen liberated at sucha cathode but there is a sub- The hydrogen not oxidized to the peroxideis oxidized to water. When no inter-electrode diaphragm is used,hydrogen peroxide finds its way to the anode where it gives up oxygenand regenerates waten.

By. providing a depolarized cathode," and by eliminating the customarydiaphragm, the overall voltage drop through the cell at a given currentis materially lowered, thereby decreasing the electrical energyconsumption. Oxidation at the anode of peroxideproduced at the cathodeyields twice as much oxygen per unit of electrical current as can beproduced by the discharge of hydroxyl ions in the absence of hydrogenperoxide. As a result, it is readily possible to produce, per unit ofenergy, over twice as much oxygen as can be produced in conventionalcells.

An example of an electrolytic cell suitable for use in practicing theinvention is illustrated in the accompanying drawing'in which:

Fig. 1 isa side sectional view, along Il of Fig. 2, of an electrolyticcell,

Fig. 2 is a top sectional view along 2--2 of Fig. 1, and

Fig. 3 is a 'side sectional fragmentary view, along 3-3 of Fig. 2,showing a detail of the cell of Figs. 1 and 2.

The cell shown in Figs. 1 to 3-comprises an outer container Ill ofcaustic-resistant insulating material, or of a metal resistant tocaustic, such as iron; 2. body of caustic alkali electrolyte H, suitablyan aqueous solution containing about 10% to 35% of potassium hydroxideor sodium hydroxide or a mixture thereof, a solution containing 25%potassium hydroxide being preferred; an insoluble or passive metal anode[2, which is preferably hollow and provided with means, such as pipes I5and I6, for circulating a coolant, and which is preferably composed ofone or more metals of the iron group (iron, cobalt, nickel); and aporous carbon cathode I3 sealed into and supported by an insulatingframe It in such a manner as to provide a space or well for the accessof air to the rear surface of the cathode l3. Above the electrolyte IIis an oxygen-collecting manifold from which oxygen may be withdrawnthrough a conduit ll. Suitable electrical connections l8 and 19 may beprovided for the anode and cathode.

The porous cathode l3 should be composed of active carbon, by which ismeant herein and in the appended claims carbon of the kind that cantransfer oxygen of the air to the cathode: catholyte interface inelectrochemically active form where it acts as a depolarizing agent. A

suitable material is that used in air-depolarized primary galvaniccells, made in any of the several known ways, and rendered resistant topenetra tion by the electrolyte. For example, the electrode materialsdescribed in Patents 2,010,608,

issued-August 6, 1935, to E. A. Schumacher, V. C. Hamister, and G. W.Heise, and 2,017,280 issued October 15. 1935, to G. W. Heise and E. A.Schumacher, are satisfactory for use in the present invention.

Although the cathode l3 shown in the drawing is a single flat plate,modifications can of course be made. For instance, an electrode of largearea may be fabricated from a number ,of smallplates, electricallyinterconnected, supported in a frame in a manner analogous to glass in amulti-paned window. Instead of a flat plate having one wet face and onedry face, a hollow carbon electrode may be used, the hollow being opento the air. Circulation of the; air to the bottom of the space behindthe cathode may be improved by blowing air through the tube 2| shown inFigs. 1 and 2.

The anode is preferably cooled because best efliciencies are obtainedwhen the cell is operated at a low temperature.

Under some circumstances, as at high current densities, it-will beadvantageous to have the depolarizing air in the space or well 20 behindthe cathode I3 under pressure.

As an example of the results obtainable by the use of the invention,operating data obtained during the use of a cell comprising a nickelgauze anode, a porous carbon air-depolarized cathode, and a 25% solutionof potassium hydroxide in water, at an electrolyte temperature of C.,are given in the following table:

A 0 th d Average, verage a o e grams of g g current oxygen per voltage pdensity kilowatthour The foregoing data indicate the general magnitudeof the increase in yield of oxygen, per unit of energy, afforded by theinvention. The electrolytic cell is of simple'construction, and can bemade of inexpensive yet durable materials. Since no hydrogen isproduced, the only loss of water is by evaporation and entrainment,there is no problem of collecting and disposing of hydrogen, nor isthere any problem of preventing the diffusion of hydrogen to the anode.There is no hazard of hydrogen explosions in the cell room.

Where electric power is cheap, and where because of intermittent orsmall demand for oxygen, or for other reasons, it is incovenient orunduly expensive to obtain oxygen manufactured by airseparation methods,the present invention provides pure oxygen at moderate cost and withinexpensive pparatus.

I claim:

1. In a, process for producing oxygen by electrolyzing an aqueoussolution between an anode and a cathode to produce oxygen at theanode,the improvement which comprises continuously depolarizing the cathodewith oxygen'to prevent the evolution of hydrogen, and promptlyelectrolyzing at the anode the product of such cathodic depolarization.1 i

2. A process for producing oxygen at a, rate upwards of 300 grams perkilowatt hour of electrical energy which comprises electrolyzing betweenan anode and a cathode an aqueous caustic alkali solution, collectingthe oxygen thereby produced, and depolarizin the cathode continuouslywith atmospheric oxygen to prevent the evolution of hydrogen, andpromptly electrolyzing at the anode the product of such cathodicdepolarization.

3. A process for producing oxygen at a rate I upwards of 340 grams perkilowatt hour of electrical energy which comprises electrolyzing betweenan anode and an air-depolarized carbon cathode n aqueous solutionessentially comprising potassium hydroxide, mingling catholyte,containing cathodic depolarization product, with the anolyte, andcollecting the oxygen thereby produced.

MILTON J ANES.

